1. Field of the Invention
The present invention relates to rotary vane actuators and in particular, the vane assembly of fluid rotary vane actuators.
2. Summary of the Prior Art
A typical rotary vane type actuator has a casing to provide a fixed volume space. The fixed volume space is separated into a first and second chamber by a rigid paddle or vane assembly. A pressurised fluid is introduced through a port into the first chamber and pressure difference between the first and second chambers produces a torque on the vane resulting in rotational movement of the vane. As the vane rotates, the pressurised fluid continues to be introduced into the first chamber to maintain the pressure.
The lower pressure in the second chamber is allowed to escape to maintain a pressure difference across the vane.
Energy is fed into the actuator by the flow of pressurised fluid and converted into mechanical work in the form of rotation of the output shaft against the torque imposed by its load.
The construction of the vane assembly is important to the efficiency of the actuator. In particular, it is important that the vane assembly provides a seal between the first and second chambers so that the energy from the input flow of pressurised fluid is efficiently converted into rotational work, rather than being wasted by leaking between chambers.
To provide this seal, a typical vane assembly has a seal made of a flexible material, such as a rubber, attached to a rigid vane. The seal is attached to the vane by a side-plate and a retaining nut and bolt extending through the side-plate, seal and vane. The seal is thus sandwiched between side-plate and vane so that the side-plate clamps the seal in position. A seal expander, made from a springy material such as steel, can also be sandwiched between the seal and side-plate and is shaped to contact and apply force to the inner surface of the seal lip and keep the seal lip in contact with the inner surface of the chamber cavity. It overcomes the problem of creep under stress of the seal material.